Modular irrigation controllers use optional modules that can be added to the controller to increase the number of irrigation stations that may be controlled by the controller. For example, U.S. Pat. No. 5,956,248 (William et al.) provides an irrigation controller having a housing that encloses a microprocessor that stores and executes watering programs, and includes station modules that can be added within the housing to increase the number of irrigation stations controlled. Additionally, U.S. Pat. No. 5,262,936 (Faris et al.) provides a controller having a base unit for actuating a predetermined minimum number of irrigation stations. External station expansion modules can be added to the base unit for increasing the number of irrigation stations controlled by the controller. Also describes are optional pump modules and accessory timer modules that behave the same as the station modules in that they provide an electrical output signal to a pump or to an accessory (such as a light), instead of to an irrigation station. However, the expansion modules in these patents simply act as additional station outputs (e.g., a conduit extension of the logic inside the controller and only include driver circuitry responsive to commands from the base unit) and do not provide any additional functionality or intelligence. In order to add functionality to these controllers apart from adding additional station outputs (e.g., to control additional stations or accessories), a user would have to purchase another irrigation controller configured with the desired functionality.
There exists, therefore, a need for an improved irrigation controller with a flexible and expandable architecture modular design, along with an enhanced communications to the modules that will provide enough flexibility for further additions to an irrigation system, not only to include additional output stations, but also to upgrade to new features and capabilities of expansion and re-configuration.